Let me say this, before you get started. If you're reading Rob MacGregor, you may want to read them in the order of publication. MacGregor was under licensing agreement not to use some of the other Indy characters we know so well, so he created some of his own (very likable characters, I might add). Throughout the series, some of these characters make various appearances and recurrences, and they build and develop off of previous adventures.
Max McCoy, on the other hand, can be read in any order. Though they do make references to other adventures in the series, it's not all that important to have read them. A sort of subplot runs through the books, though, stemming from a crystal skull Indy finds in the first novel of McCoy's series. The last novel does a nice job of tying the subplots together, and it's nice to see Indy confronting the curse of this skull in each novel.
Omit Caidin.
For plot descriptions, you can search for the novel on Amazon.com and read about it there. "Hollow Earth" was a great one, though. There are only 3 novels in the entire series that I would be wary of recommending without reserve: Martin Caidin's two (which will remain nameless), and Rob MacGregor's last installment, "Indiana Jones and the Interior World." This book was extremely weak and relied heavily on characters from another dimension of reality that gain access to our world through a sort of temporal/physical displacement portal. Very unlike Indiana Jones plots, and somewhat strange. The dialogue seems a bit lacking, too.
Good luck, and let me know how the reading goes!